Problem: Omar ate 3 slices of pizza. Ishaan ate 4 slices. If Omar ate $\dfrac{3}{10}$ of the pizza, what fraction of the pizza is remaining?
If 3 slices represent $\dfrac{3}{10}$ of the pizza, there must have been a total of 10 slices. $\text{fraction of pizza remaining} = \dfrac{\text{number of slices remaining}}{\text{number of slices total}}$ Together they ate 7 slices, which leaves 3 out of 10 slices remaining. There is $\dfrac{3}{10}$ of the pizza remaining.